1. Field of the Invention
The present invention relates generally to structures for connection of a multiphase superconducting cable including a plurality of cable cores having superconductor, and multiphase superconducting cable lines including the structure, and particularly to such structures capable of positionally stabilize a conductor connect in a connection box, and such lines including the structure.
2. Description of the Background Art
As one of superconducting cables that have been produced using a superconductor formed of a bismuth (Bi)-based high-temperature superconducting tape for example, not only a single-phase cable including a single cable core but a multiphase superconducting cable of multicore type that is produced by assembling a plurality of cable cores into one unit is also under development. FIG. 6 shows a 3-phase superconducting cable of 3-core type in cross section. With reference to the figure, this superconducting cable 100 includes three cable cores 102 twisted and accommodated in a thermal insulation pipe 101.
Thermal insulation pipe 101 has an outer pipe 101a and an inner pipe 101b. This double pipe constructed of these outer pipe 101a and inner pipe 101b has a thermal insulation material (not shown) provided therein and a vacuum is produced within the double pipe. These cable cores 102 each include, in the order starting from the innermost component, a former 200, a superconductor 201, an electrical insulation layer 202, a shield layer 203, and a protection layer 204. Superconductor 201 is constructed by winding superconducting wires around former 200 in a spiral manner in layers. Electrical insulation layer 202 is formed of wound polypropylene laminated paper. Shield layer 203 is constructed by winding superconducting wires similar to that of superconductor 201 around electrical insulation layer 202 in a spiral manner. In this shield layer 203, in a steady state, current is induced of almost the same magnitude as and opposite in direction to current flowing through superconductor 201. The induced current causes a magnetic field to be generated that cancels out a magnetic field generated from superconductor 201 to achieve almost zero leakage magnetic field outside cable core 102. A space 103 formed between inner pipe 101b and each cable core 102 usually provides a path where a refrigerant flows.
If such a multiphase superconducting cable is used to construct a line over long distance, the line requires an intermediate connection connecting together cable cores extracted from different cables. Such intermediate connection has a structure described for example in Japanese Patent Laying-Open No. 2000-340274 (see FIG. 1). In this structure, superconductors accommodated in a connection box have their respective ends connected in a connection sleeve and a stress cone is attached to the superconductors' ends and the connection sleeve's outer circumference and supported by a rod formed of fiber reinforced plastics (FRP). Furthermore the cable cores in the connection box are supported at a splitter portion of FRP.
For the above described, conventional structure, however, a connection of a superconductor of a cable core in the connection box may for example be positionally moved from a prescribed position, resulting in a disadvantageously variable location for installation.
A superconducting cable is cooled by a refrigerant, as has been described previously. This contracts the cable and accordingly moves the superconductor. As the superconductor moves, in the connection box a portion of each cable core that connects the conductor may each positionally displace as seen lengthwise. Japanese Patent Laying-Open No. 2000-340274 describes a structure providing a connection box accommodating a cable core, a stress cone and the like supported by an FRP member. However, the contractive force exerted as the refrigerant cools the cable is in a significantly large order of several tones, and the FRP member can hardly prevent the movement of the portion that connects the conductor that is associated with thermal contraction. Accordingly, the portion can disadvantageously move from the location for installation.
Furthermore if a cable installed has a condition the portion that connects the conductor is disadvantageously moved toward one side of the connection box or similarly, not positioned in the box, as prescribed. Conventionally there has not been any known effective structure addressing this disadvantage.